This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Recent biochemical work by Thauer allowed for the structural characterization of the active site in [Fe]-hydrogenase. This hydrogenase is unique in a sense that it does not contain Fe-S clusters like the [FeFe]- and the [NiFe]-hydrogenases. However, it shows a common active site structural motif for the presence of diatomic ligands which is likely carbon monoxide. The hydrogenases are the only family of enzymes that contain this otherwise toxic ligand to living organisms. We are proposing a series of multi-edge x-ray absorption measurements to fully characterize the electronic and geometric structure of several biomimetic compounds. Our data will allow for the refinement of several uncertainties with the active site in composition, electronic, and geometric structure. Furthermore, the XANES and EXAFS data will allow us to validate electronic structure calculation methods that are to be used to map the molecular mechanism of the H2-forming methylenetetrahydromethanopterin dehydrogenase.